From: Pit Capitain <pit@...>
Date: 2006-09-21T16:54:56+09:00
Subject: Re: Creating ruby-serialport singleton object breaks

Adam Block schrieb:
> I'm trying to create a singleton serial port class with the following 
> code:
> 
> require 'serialport'   # version 0.6
> require 'singleton'
> 
> class SerialConnection < SerialPort
>   include Singleton
> 
>   def initialize
>     sp = super("/dev/tty.KeySerial1", 9600, 8, 1, 0)
>   end
> end
> 
> But when I try to create the instance it breaks:
> 
> irb(main):009:0> sp = SerialConnection.instance
> ArgumentError: wrong number of arguments (0 for 1)
>         from (irb):8:in `new'
>         from (irb):8:in `new'
>         from /usr/local/lib/ruby/1.8/singleton.rb:95:in `instance'
>         from (irb):9

Adam, the problem is that SerialPort.new requires at least one argument, 
but Singleton.instance calls new without any arguments. You supply the 
missing arguments in SerialConnection#initialize, but this is too late, 
because SerialPort.new is called before SerialConnection#initialize. 
Change your code to

   class SerialConnection < SerialPort
     def self.new
       super("/dev/tty.KeySerial1", 9600, 8, 1, 0)
     end

     include Singleton
   end

and it should work. Note: in order to avoid a warning about redefining 
SerialConnection.new, you have to include Singleton *after* defining the 
method.

Regards,
Pit